1. Field of the Invention
A dust or stone shield of the type forming the subject matter of this invention is designed to surround the pushrod of a fluid operated service brake actuator to operate as a barrier to block entry of contaminants into the actuator housing.
2. Description of Related Art
Dust or stone shields of the type noted are designed to surround pushrods of fluid operated service brake actuators. Typically, this sort of shield operates as a barrier to block entry of contaminants that might otherwise pass from outside an actuator housing, through a gap between a pushrod outer circumference and a pushrod opening in an actuator wall, and into an interior of the actuator housing, such as a chamber providing for expansion and contraction of a service brake pressure volume. In such an arrangement, the shield commonly has an inner diameter surrounding the articulating pushrod at the very location at which side loading of the pushrod occurs. For most rigid shields, shield inner diameters have been accepted as load bearing interfaces. In such a construction, if the inner diameter of a shield is compromised by side loading, the shield may no longer operate effectively.
Conventional pushrod dust or stone shields for chambers with threaded pushrods lack slits or slices in them. When such a shield is to be used with a welded clevis, it is not possible to drop the shield over the end of the pushrod. To address this issue, some shields now used with welded devises have slits or slices to facilitate fitting the shields over respective pushrods. Single-slit designs have been the accepted standard, regardless of assembly difficulty and part stress.
U.S. Pat. No. 6,354,187 to Plantan et al. concerns a known arrangement in which an annular damping stone shield has a slit allowing assembly around a pushrod. An annular groove in the stone shield circumscribes the push rod opening and allows the shield to absorb lateral forces when the push rod is operated during braking.
U.S. Pat. No. 6,729,224 to Roy discloses various configurations of an annular ring surrounding a pushrod when assembled. In one such configuration, the ring has end surfaces that are angled relative to the shaft opening axis of the ring. The angled end surfaces are configured so that the return spring can bias the slit opening in a closed position to create a seal, thereby preventing contaminants from entering the brake chamber.
U.S. Pat. No. 5,320,026 to Pierce, U.S. Pat. No. 5,392,691 to Schultz, U.S. Pat. No. 5,450,930 to Martens et al., U.S. Pat. No. 6,267,043 to Plantan et al., U.S. Pat. No. 6,314,861 to Smith et al., U.S. Pat. No. 6,318,240 to Plantan et al., U.S. Pat. No. 6,360,649 to Plantan, U.S. Pat. No. 6,480,107 to Stonehocker et al., U.S. Pat. No. 6,501,375 to Weant et al., and U.S. Pat. No. 6,753,771 to Lesesky are also of interest.